1. Field of the Invention
The present invention generally relates to a semiconductor device and its manufacture method, and specifically to a semiconductor device with a polycrystalline semiconductor layer and a method of forming a polycrystalline semiconductor layer. Polycrystalline semiconductor layers are used in liquid crystal displays, solar batteries, and the like.
2. Description of the Related Art
A conventional technique of forming a polycrystalline semiconductor layer will be described by taking as an example, a method of forming a polysilicon layer on a glass substrate.
It is known to polycrystallize a thin film of amorphous silicon deposited on a glass substrate by performing heat treatment at about 600.degree. C. Since this method requires heat treatment at about 600.degree. C., the glass substrate may be deformed with heat. Crystal grains in the polycrystallized silicon thin film contain many stacking faults and twins so that it is difficult to form a film having good crystallinity.
Another known technique is to melt an amorphous silicon thin film by applying an energy beam, such as a laser beam, and polycrystallize it while it is cooled. This method requires a high density of laser energy in order to obtain polycrystals of high quality. However, if the laser intensity is too strong, it is difficult to obtain a polycrystalline film uniform in quality because of an unstable operation of a laser source system or other reasons.
Chemical vapor deposition (CVD) may also be used for the formation of a polycrystalline silicon film. Also in this method, a growth temperature of 600.degree. C. or higher is necessary which may cause deformation of a glass substrate. With this method, it is also difficult to obtain a silicon film good in crystallinity.
As above, conventional techniques are difficult to form a polycrystalline semiconductor layer good in crystallinity, on a glass substrate, for example.